The following relates to the lighting arts. It finds application for example in general illumination, accent lighting, architectural lighting, and so forth.
The combination of light emitting diode (LED) devices with wavelength-converting phosphor has well understood advantages. LED devices generally emit light over a relatively narrow spectral range, which is not suitable for typical illumination applications. By coupling LED devices with wavelength converting phosphor, light of broader spectrum can be generated, including various spectrums corresponding to white light.
However, it has also been recognized that a difficulty with this combination is that the phosphor can degrade over time. Phosphor degradation has been observed in various LED/phosphor combinations, and is particularly problematic in white devices that combine an LED emitting in the blue, violet, or ultraviolet range with a white phosphor composition. Phosphor degradation typically results from heating. A known solution is to place the phosphor remotely from the LED die. An example of such a device is set forth in U.S. Pat. No. 7,224,000.
Remotely positioned phosphor address the problem of heat-induced phosphor degradation. Additionally, for most applications the arrangement has the further advantage of spreading out the illumination over the area of the remote phosphor, so as to provide wide angle illumination.
For some applications, however, narrow angle illumination is desired. Such applications include, for example, accent lighting intended to “wash” a wall with light, lighting intended to track a walkway, formation of a free-standing planar “wall” of light, or so forth. Existing LED/phosphor combinations are generally not well-suited for such applications. For example, providing a linear array of phosphor coated LEDs or of LED/remote phosphor combinational elements such as those disclosed in U.S. Pat. No. 7,224,000 would provide a linear light source, but one which emits illumination over a relatively broad angular range.